Sodium percarbonate is a well-known bleaching ingredient in detergent compositions and is widely disclosed in the literature, although in recent years its use in commercial products has been abandoned in favour of sodium perborate. Sodium percarbonate is less stable than sodium perborate in the presence of moisture, and its stabilisation in detergent powders has long been recognised as a problem to which various solutions have been suggested; for example, GB 1 515 299 discloses the stabilisation of sodium percarbonate in a detergent composition by admixture with a perfume diluent, for example, dibutyl phthalate.
The problem becomes especially acute if sodium percarbonate is to be included in a detergent powder with a high free moisture content, when it tends to become deactivated on storage. This situation applies in particular to powders containing crystalline alkali metal aluminosilicates (zeolites), because those materials contain a large amount (about 10-15 wt % in zeolite 4A, for example) of relatively mobile water.
Detergent compositions containing alkali metal aluminosilicate (type 4A zeolite) and sodium percarbonate are disclosed in DE 2 656 009A (Colgate), in Examples 1 and 2, but storage stability is not discussed. According to GB 2 013 259A (Kao), the problem of sodium percarbonate stability in the presence of hydrated crystalline zeolites is solved by the use of an amorphous or partially crystalline aluminosilicate (0-75% crystallinity) or by the use of a partially calcium- or magnesium-exchanged material. However, use of such special aluminosilicates is clearly less convenient, and probably more expensive, than the use of the widely available crystalline zeolite 4A.
Laundry treatment products in the form of two-compartment sachets containing bleaching detergent compositions are described in the art. One such product, containing sodium perborate, is sold commercially in Italy.
US 4 410 441 discloses a two-compartment sachet of water-insoluble material for sequential dosing of particulate detergent ingredients to a wash liquor. One compartment contains a non-bleaching detergent composition, while the other compartment contains sodium perborate tetrahydrate. Release into the wash liquor is by leaching out through water-insoluble water-permeable sachet walls.
GB 1 538 744 (Interox) discloses bleaching compositions containing diacyl peroxides which, according to a passing reference, can be isolated from alkaline surfactants by enclosure in a flexible sachet which may also contain sodium perborate or sodium percarbonate.
GB 1 505 274 (Colgate-Palmolive) discloses detergent compositions in the form of a plurality of small dosage units, for example sachets but preferably and specifically tablets, containing different ingredients that can be dosed individually by the consumer. A detergent tablet system is described (Example 6) consisting of a detergent tablet (surfactant, builders, fluorescer, colourant), a builder tablet (additional builder), and a bleach tablet (sodium percarbonate and nonionic surfactant).
Bleaching detergent compositions contained in water-soluble sachets are also disclosed in the art, for example, in US 3 322 764 and US 3 186 869 (Friedman) and EP 79 248A.
There is a problem associated with the packing of detergent compositions containing sodium perborate in sachets of polyvinyl alcohol film, otherwise the most popular film material for water-soluble sachets: polyvinyl alcohol tends to be insolubilised by the borate ions generated in the wash liquor by decomposition of the sodium perborate, so that the sachet can become insufficiently soluble to release its contents during the wash cycle; or at least can leave unpleasant undissolved residues among the washed fabrics. EP 79 712A (Clorox) discusses this problem and suggests various modifications of the polyvinyl alcohol film material itself in order to increase its solubility in the presence of borate ions.
GB 836 108 (Henkel) discloses a bleaching detergent composition containing a percompound (preferably and specifically sodium perborate) and an activator. The activator, and if desired the percompound, can be separated from the remaining ingredients by wrapping in a water-soluble film.
A product now commercially available in France consists of a phosphate-built detergent powder containing sodium percarbonate sealed into a single-compartment sachet of water-soluble polyvinyl alcohol. Each sachet is provided with a small number of pinholes so that any oxygen generated by percarbonate decomposition can escape without bursting the sachet. A zeolite-built variant recently introduced by the same manufacturer, however, contains no sodium percarbonate.
EP 253 566A (Procter & Gamble) discloses multilayer sachets (water-soluble polyethylene oxide film with outer covering of water-permeable nonwoven fabric) containing bleaching detergent compositions. Some two-compartment sachets are disclosed, but, unless organic peracids are present, the contents of all compartments are identical. No products containing both zeolite and sodium percarbonate are disclosed.